TOCTTOU in usage of access()

[guijan]

https://en.wikipedia.org/wiki/Time-of-check_to_time-of-use

There's no guarantee that the information access() returns is valid after it returns.

This function should be removed and its caller should be reworked to use open():

proxychains-ng/src/common.c

Lines 77 to 81 in d5cc80a

	static int check_path(char *path) {
	if(!path)
	return 0;
	return access(path, R_OK) != -1;
	}

There's a 2nd usage of access() in the source code, but it's not a bug because there's no way to do what it does with file descriptors:

proxychains-ng/src/main.c

Lines 122 to 129 in d5cc80a

	while(dll_dirs[i]) {
	snprintf(buf, sizeof(buf), "%s/%s", dll_dirs[i], dll_name);
	if(access(buf, R_OK) != -1) {
	prefix = dll_dirs[i];
	break;
	}
	i++;
	}

[rofl0r]

i'm aware about TOCTTOU and its implications, but i figure the chances of proxychains.conf disappearing between the check and the usage are too small to be relevant.
in all the years maintaining this program this theoretical issue not once surfaced in a practical issue report.